1. Field of the Invention
The present invention relates to grafted ethylene copolymers and use thereof as additives for inhibiting the deposition of paraffins and improving the flow properties of crude oils and also relates to the compositions containing the oils and said additives.
Crude oils may contain appreciable paraffin fractions, the amount and exact nature of which are variable depending on the extraction fields. At the temperature of the well the paraffins are liquid and dissolved in the crude oil. When the oil is raised to the surface, its temperature drops and the paraffins, by crystallizing, form a three dimensional network of needles and scales. The result is a loss of fluidity which makes the production, transport, storage and even processing of these oils very difficult. Clogging up of the ducts and processing apparatus is frequent.
2. Description of the Prior Art
Numerous processes have been proposed for resolving this clogging problem, such as mechanical scraping or heating the walls of the ducts or processing apparatus. These processes are costly and use thereof is not always possible.
The use of additives has also been suggested. Polymeric additives whose role is to retard or modify the crystallization of the paraffins and thus to improve the flow properties of the oil and to prevent caking of the crystals formed on the walls are known.
Among the polymeric additives may be mentioned the ethylene-vinyl acetate copolymers, (EVA) described in the French certificate of utility No. 2 184 522 (1972) of Union Oil of California. These polymers have an effect on the starting crystallization temperature of the paraffins but are inefficient for dispersing the crystals already formed. They also have the drawback of being only slightly soluble in the crude oils.
Attempts have been made to improve the efficiency of the EVA copolymers by adding other polymers. Thus, the British Pat. No. 1 112 803 (1966) belonging to ESSO describes the use of a synergic EVA copolymer mixture with polyacrylates.
In order to improve the dispersing effect of these additives as well as their solubility in the crude oils the use of statistical copolymers of ethylene, vinyl acetate and other monomers is recommended. Hereafter we will use the term copolymer for designating the polymers formed from at least two monomers.
Thus the Soviet Pat. No. 785337 (1978) describes ethylene, vinyl acetate and maleic anhydride copolymers. The U.S. Pat. Nos. 3,341,309 (1967) and 3,304,261 (1966) of ESSO recommend the use of ethylene, vinyl acetate and dilauryl or diisodecyl fumarate copolymers. The U.S. Pat. No. 4,160,459 (1977) of TEXACO relates to ethylene, vinyl acetate and alkyl methacrylate copolymers.
However, in these copolymers the monomers are incorporated statistically in the polyethylene chain. The result is a reduction in the length of these chains, which causes a decrease of affinity for the paraffins and adversely affects the efficiency of the product as a crystallization inhibitor.
The present invention overcomes these drawbacks and provides a series of additives having good solubility in crude oils, which have an effect not only on the crystallization of the paraffins but also on the dispersion of the crystals already formed.